I had this piece of jewelry appraised in 1994 for $860.00. It's a 14 karat yellow gold freeform pendant, containing 1 round brilliant cut cubic zirconia stone, prong set. Today I went to a jewelry store to sell it. They told me this is not worth anything, it is costume jewelry. Why at one time it was appraised for $860.00 & now this store says it's worthless? Please help.